3A. Indexing

{ encompasses everything performed by bracket indexing
in other languages.
The ranks are 0 _ , that is, x{y can be considered individually
for each scalar in x and for y in toto,
with the overall result constructed from the individual results in the same way
as for all other functions. For scalar x then:

>x is a scalar or a list, and r=:>j{,>x
are the indices for axis j . r may be integers
in the range i.&.(+&n)n=:j{$y ,
which selects cells n|r ,or r
may be boxed integers in that range,
in which case the selected cells are all except those in n|r . Thus: